A2338 820-02020 PP3V8_AON Shorted

[Instafixx]

Board Seemed to have gobe through an ultrasonic cleanse.

PPBUS_AON is 12.3V
AMP Meter Stuck at 5V.
PP3V8_AON is shorted. Diode mode reading .002

Found LR503 to be getting hot after injecting voltage.
Removed LR503. 3V8_AON is now .360 (Diode to Ground).

But PP3V8_CODEC_VP is still shorted.
Removed UR500 the short is gone.

Before Replacing - tried to see if the i get 3V8_AON voltage but it is still 0V.

P3V8AON_PWR_EN IS 5V
CHGR_EN_MVR IS 5V.

 

[2informaticos]

Check voltage at U5700, pins 5, 6, 7.

 

[Instafixx]

Pin 5/7 is 5V
Pin 6 is 0V

Diode Mode to Ground is .056

PP5V_S2_P3V8AON_VDRV

Reading Across Pins
R5900 is 0.5 Ohms
C5700 is 38 Ohms

Removed R5900.

PP5v_S2 is shorted with Diode Mode 0.056

P5VS2_EN
DIODE Mode Reading is .366
Voltage is 0.

PPVIN of UC300 is same as PPBUS.

UC300 looks dirty also on the borders pins. Removed it. Still Short Remains.

Injected Voltage at PP5V_S2. i dont know how but short removed. I get around .350 value to ground.

Put Still Pin 6 of U5700 is 0V

 

[2informaticos]

Still missing 5VS2_EN?

Something is damaged on the 5V_S2 power rail.
Possibly corrosion on its feedback network; that can cause random overvoltage.

 

[Instafixx]

Yeah still missing

 

[2informaticos]

"Injected Voltage at PP5V_S2"
How much voltage directly?
If inject high voltage, can burn the culprit without noting it.
The idea is to start with low voltage (1V) and check if something gets hot; increasing the voltage, if need.

 

[Instafixx]

Started with 1V. But nothing got hot.
Gradually increased it step by step to ultimately 3V. The current draw was very low.
I have a 5A PSU.

 

[2informaticos]

You can go up to 5V; may have luck and find some signature with IR cam.

 

[Instafixx]

But the short has removed. Will anything get hot?

 

[2informaticos]

No short anymore, but something may be affected.
A good thermal camera may help you; worth to try.

 

[Instafixx]

I went upto 5V but the current draw is 0.007 Amps. Nothing gets hot at all.

Any suggestion what to do ?

 

[Instafixx]

Ohms Value Between Pins

CC335/CY131/CY130/CC334//CC337 - 1.2K OHMS
LC320/RC327 - 0.5 OHMS
RP844 - 180 OHMS
RP 845 - 11 OHMS
RP852/853 - 1.3 K OHMS
CP717 - 1.3 kOhms
CE504 - 1.3 kOhms
LT700 - 4 Ohms
R5900 -0.9 Ohms

RP844 seems off. Replace it. Now Ohms Value is 1.5 Ohms. But voltage situation is the same.

 

[2informaticos]

3V8_AON present now?

 

[Instafixx]

Nope.

 

[2informaticos]

Must fix that first.
Post U5700 voltages: VIN, LDO5, PVCC, ENABLE.

 

[Instafixx]

PPBUS_VMAIN_VIN_ISNS - 12.3V
PP5V_AON - 5V
P3V8AON_PVCC - 5V
P3V8AON_PWR_EN_R - 5V

 

[2informaticos]

If no short on 3V8_AON power rail, then change U5700.

 

[Instafixx]

Replaced. Still the same

 

[2informaticos]

Check all Q5800/20/40's adjacent components.
Compare diode mode readings around U5700 and Q5800/20/40 with good board.

 

[Instafixx]

I dont have a Good Board.
But while checking with OpenBoard Data

Diode Mode Readings to Ground which seem off

R5825/6 is 1.02
P3V8AON_BST2_RC - .976
P3V8AON_BST3_RC - .976.

Should i check further ?